Reading usernames from the Twitter file

GettingUsernames.py

import sys
import os

with os.popen('zcat ' + sys.argv[1]) as tweet_file, open(sys.argv[2], 'w') as output:
        #skip all lines with anything but U in them 
        for line in tweet_file:
                parts = line.rstrip().split('\t')
                if 'U' not in parts[0]:
                        continue
                output.write(parts[1].lstrip('http://twitter.com/') + '\n')